Space-based solar power, part 2: running the numbers

The coolest technology in the world doesn't make any sense if it's too …

PowerSat isn't the only company that thinks space-based solar power will be ready for economic deployment within the next decade. PG&E has actually signed a contract with a company called Solaren, which plans on delivering 200MW of space-based power by 2016. The company already has two patents for space-based systems, although both are extremely general, and the company hasn't publicly discussed the details of its plans. Nevertheless, it's clear they differ significantly from those of PowerSat, and those differences highlight some of the tricky economics of space-based solar power.

PowerSat's William Maness is moving in a different direction from Solaren. One of his biggest issues with such schemes is the location: serving spots like southern California, which already has excellent access to some of the best terrain for standard solar power within the US, doesn't make sense to him.

"If you can build productive ground-based facilities, it generally makes more sense to do that," Maness said. Instead, PowerSat will target markets that have strong renewable power mandates but less favorable options for ground-based solar; the Pacific Northwest and New Jersey were both mentioned explicitly.

He also prefers to avoid contracts for dedicated supply. Because ground facilities are relatively inexpensive, it would be possible to build several, and switch the satellites' target among them, pushing the power to wherever the company can get the best rates.

And avoiding smaller contracts is important, since the power provided is below the point where efficiencies and economies of scale really apply. In PowerSat's view, a large-scale, space-based solar facility with a 30-year life span provides the renewable energy equivalent of a large coal or nuclear plant, and has to be evaluated along those economic lines. Maness claimed that PowerSat's calculations indicate that, depending on governmental renewable power incentives, the total returns over 30 years work out to be similar to a large coal plant once fuel and waste disposal are considered, and they are somewhat better than nuclear.

All of that still requires launch costs to come down, however. Because of the satellite's modular design, Maness said they can go up on anything with a minimum of 10-ton launch capacity; larger vehicles would simply carry multiple satellites. That lets the company shop for the cheapest ride to low-earth orbit. Right now, PowerSat is seeing some of the best rates from SpaceX, a private company that has performed several launches. By the time PowerSat is ready for launches, SpaceX should have several years of experience with providing supply flights to the International Space Station as part of a contract with NASA.

Even so, Maness suggested costs need to come down to between a third and a quarter of current rates. But he argued that his company's plans have the sort of profile that could make that happen. The plan is to build multiple satellites in advance, then run an intensive launch schedule that ensures the generating capacity scales rapidly. That should get launch companies past what he called the "chicken and egg problem": launches are expensive because there's little economy of scale, and the expense scares away customers that could drive economies of scale. Maness also pointed out that electric utilities come to the table with a credit worthiness that's been rare in space-based businesses.

PowerSat's Philip Owen also suggested there might be a customer that can get at least some of the hardware into orbit even if launch costs don't come down: the military. He noted that it's possible to build smaller receiving stations that won't be able to extract the full output of the microwave transmissions, but could easily provide enough power to keep a modern military's electronic gear online. Given the problems with cost, logistics, and security that come with supplying fuel to the generators used during field deployments, space-based power could make economic sense for the military at levels where it doesn't for civilian use.

Because of the flexibility of targeting, it may be possible to have satellites deployed for testing and training purposes, but then redirect their output to civilian power production when they're not in military use. And that could change the economics for putting up companion satellites that are dedicated to civilian use.

In any case, it's clear that PowerSat has crunched the numbers and found some scenarios where orbital power can make sense. The key determinants will be whether any of the company's numbers are overly optimistic, and whether the essential features of those scenarios—lower civilian launch costs, increased renewable energy standards—are in place by the middle of the next decade.

95 Reader Comments

"Given the problems with cost, logistics, and security that come with supplying fuel to the generators used during field deployments, space-based power could make economic sense for the military at levels where it doesn't for civilian use."

And how long will the satellite take to move from a geosynchronousstationary orbit over Bad Guy Land back to the Good Ol' US?

It's an interesting idea; though I'm wondering, if they're supplying power via microwave, what are the risks of missing the station? Are we talking something with the intensity to harm someone on the ground?

Originally posted by protomech:"Given the problems with cost, logistics, and security that come with supplying fuel to the generators used during field deployments, space-based power could make economic sense for the military at levels where it doesn't for civilian use."

And how long will the satellite take to move from a geosynchronous orbit over Bad Guy Land back to the Good Ol' US?

Forget supplying power, just use it as a weapon against Bad Guy Land. Yay for microwaves!

If the power transmission screws up radio communications, and it probably isn't friendly for anything that has an antenna, like RADAR, wouldn't that make a lot of it's use for powering military electronics rather...dumb? You could set up the receiving station a distance away but then you are back to having a supply line to create and protect.

Am I the only one concerned that an orbital microwave could easily be turned into a weapons systems if need arises? Or, if there's a malfunction in targeting...well, half a neighborhood could get fried?

Originally posted by Tundro Walker:Am I the only one concerned that an orbital microwave could easily be turned into a weapons systems if need arises? Or, if there's a malfunction in targeting...well, half a neighborhood could get fried?

Originally posted by whquaint:The airplane question is a good one I haven't heard before. What would the microwave beam do to an airplane flying through it?

Cook its onboard mealcart? Ok, and maybe the crew. Kidding, the last thread already established that they wouldn't use the cooking frequencies (tuned to water and fat resonance at 2.45 GHz). Obviously.

Seriously though, with all the FAA regulations and control towers and (post-2001) national security rules, planes wouldn't go near it. Period. The same way they don't fly into hurricanes (except for those crazy storm-chasers).

Originally posted by Tundro Walker:Am I the only one concerned that an orbital microwave could easily be turned into a weapons systems if need arises? Or, if there's a malfunction in targeting...well, half a neighborhood could get fried?

How much energy is lost through transmission, and does inclement weather affect efficiency?

And what about space based solar thermal using inflatable mirrors? Seems it would be much cheaper to use Mylar or whatever than manufacturing inflatable solar panels, even when thin film tech. I guess the biggest concern would be radiating the heat away, and carrying all that radiator weight into space. The benefit is that there is a huge temperature differential, and using a sterling engine, efficiency per surface area could be much much higher than thin film.

<just brainstorming, but maybe the radiator could be inflatable too. have a flowing working fluid, and then have another fluid that is pumped into thin plastic tubes and freezes into a radiator shape behind the mirrors. the working fluid flows through channels in the now solid radiator. this could allow a huge surface area without having to pack a solid structure in the launch vehicle.>

edit: ok i just thought of what may be a problem: fluids in zero gravity. probably not an insurmountable engineering problem, though.

edit 2: How about an inflatable mirror used to focus light on a photovoltaic plant on the earth throughout the night? not greater-than-daylight focusing, so you wouldn't be cooking birds and such, but I guess light pollution would be a complaint

Even if this works, this is one of those cases where I am not sure why the patents were filed. A patent only has a 20 year life and it is somewhat optomistic to expect this sort of solar plant to happen before 2020 so you are talking about limited return on the investment. Furthermore, patents are geographic so it is unclear how a satelite in space is infringing anyone's IP in the world. I guess you could argue that the US controls the space directly above the US but it seems like it would be relatively simple to position the satelites on the edge of a country and still be fairly effective. Maybe they plan to have some method claims. Furthermore, a patent is used to create an barrrier to entry, the cost of getting the stuff up in space seems like enough of a barrier - if you can come up with the billions to get off the ground you can probably figure out a way to avoid infringement...

It is a neat idea as it potentially solves the interrupted nature of ground-based solar but for my money there are better ways to get power and given the problems with the side effects of power transmission I think it only partially helps the distribution issues. Also, you have to wonder how much CO2 is saved when you have to launch 10 tons - rockets create a significant amount of CO2. Maybe the numbers make sense but this seem pretty pie in the sky to me.

They want launches to get cheaper? Fat chance. The only reason they are so cheap at the moment is because the old Russian ICBMs were converted to launch vehicles and flooded the market. As they get used up prices will increase.

Edit: And ++ to where are the numbers? over-promised and under-delivered.

Regarding NJ -- wouldn't it make more sense to build off-shore wind turbines? Also, NJ is the hghest population density state in the US --- where are they going to put the receivers? What will the land cost?

Regarding military applications -- if these satelites provide power for the military then they become military targets. Let's think whether that really makes sense.

Edit -- one more thought -- this whole thing reminds me of Iridium. Let's ask motorola how well that worked out

Originally posted by whquaint:What would the microwave beam do to an airplane flying through it?

Cook its onboard mealcart? Ok, and maybe the crew. Kidding, the last thread already established that they wouldn't use the cooking frequencies (tuned to water and fat resonance at 2.45 GHz). Obviously.

Seriously though, with all the FAA regulations and control towers and (post-2001) national security rules, planes wouldn't go near it. Period. The same way they don't fly into hurricanes (except for those crazy storm-chasers).

This is what running the numbers is for. Any aluminum skin that's airworthy is more than enough to block in this band, and a pressurized cabin is pretty much a Faraday cage. Well, passenger windows don't view space; the cockpit windows may need metal deposition, but the few cockpit windows should make this manageable. In terms of secondary effects, planes have emitters as lightning rods, which is way worse that this beam. Lightning protection is also why composite planes are safe- the plane, at least; if the material spec is unlucky, we may have to make sure harness and ducting add enough metal to screen the cabin. And, of course, this is what air traffic control is already doing, even over the countryside.

Disrupting the RF gear, as mentioned in the article, is probably the real issue. How does the article figure compare to a cell phone?

Originally posted by PsionEdge:They want launches to get cheaper? Fat chance. The only reason they are so cheap at the moment is because the old Russian ICBMs were converted to launch vehicles and flooded the market. As they get used up prices will increase.

Yes and no. The sweetest setup is Soyuz and other R7-based launchers. The missiles were a failure, and pulled after a couple of years, but the factory chugs on. The actual R7 missiles got used up... oh, I'd say... '67.

Later missiles certainly get re-aimed to space every now and then, but not as often as you think. First, both Moore's law and new materials science caught up with them, and they're significantly smaller than the first-generation missiles. This makes them too small for most satellites, and way way WAY too small for what we're talking here. There are plenty of them left, if you can shrink your satellite to the size of a warhead or two- pretty small.

Originally posted by The Real Blastdoor:Regarding NJ -- wouldn't it make more sense to build off-shore wind turbines? Also, NJ is the hghest population density state in the US --- where are they going to put the receivers? What will the land cost?

That says more about the US than it does about New Jersey. There's significant room in NJ because, if I may over-generalize, the US has significant room EVERYWHERE.

quote:

Regarding military applications -- if these satelites provide power for the military then they become military targets. Let's think whether that really makes sense.

Meh. Hitting a target in GEO is a different beast than hitting one in LEO. Not impossible, of course, just way harder.

quote:

Edit -- one more thought -- this whole thing reminds me of Iridium. Let's ask motorola how well that worked out

Now that's the big issue. IANA solid-state physicist, but the question I'd ask is whether some next-generation PV technology or work fluid is kicking around some lab somewhere, and will pull the rug out under a whole bunch of startups. Iridium pretty much fell to adding more towers (I'm oversimplifying of course).

Iridium failed because the reality was that most people did not need phone service coverage over 100% of the entire globe. When's the last time you made a business trip to Antarctica? The economics just weren't there compared to terrestrial phone systems, landline or wireless.

That says more about the US than it does about New Jersey. There's significant room in NJ because, if I may over-generalize, the US has significant room EVERYWHERE.

I live in the Princeton area and I don't see where this "significant room in NJ" is. The land that doesn't have shopping malls or houses on it is generally protected green space owned by townships dedicated to not developing the land (good luck navigating the overlapping bureaucracies of local govt in NJ if you want to use that land for anything -- local govt here is insane). The closest area with land that might (maybe) be close to cheap enough is in PA. But even then... I think you'd have to go kind of far into PA to find land that's cheap enough to use for this purpose, and given population growth, I don't know how long it will stay cheap.

I think the best bets for NJ are offshore wind and nuclear, plus maybe a national smart grid to hook us up to more wind resources further west. I'd much rather spend money on a smart grid than solar satellites.

Originally posted by The Faceless Rebel:Iridium failed because the reality was that most people did not need phone service coverage over 100% of the entire globe. When's the last time you made a business trip to Antarctica? The economics just weren't there compared to terrestrial phone systems, landline or wireless.

And I think similar realities apply here, too. What's easier -- launching a satellite into space or putting a solar panel on a roof or a wind turbine up a few hundred miles away?

We don't need power beamed down from space when we have wind and solar resources down on the ground. Upgrading the grid would likely cost less than launching huge numbers of satellites into space. And repairing wires downed by a hail storm is a lot easier than repairing satellites hit by space junk.

The backers of Iridium were fully aware of the existence of cell towers. But they somehow convinced themselves that economies of scale in launching satellites combines with the appeal of universal coverage would win out. It didn't.

I think that some people have a huge blind spot when it comes to anything involving space. Maybe it's Gene Roddenberry's fault, I don't know. But somehow spending twice as much money on something that is 1/2 as effective seems appealing so long as "space" is involved. For example, some people would rather spend tens of billions of dollars to put a human bootprint on Mars than spend the same money to build out a national electric grid or invest in more biofuels research.

@Maury and others, primarily addressing the practicality of the PowerSat modules.

This is a reply to Maury first post, mostly. I've missed the resulting discussion since I was writing and researching it....

There are three primary weaknesses to your discussions with regards to PowerSat and SSP in general: 1) You don't consider the trade-offs between panel effeciency, panel weight, and panel production cost and capacity. You pick a point based on effeciency alone. It may not be the best point, and PowerSat clearly disagrees, going with thin film CIGS cells.

2) You dismiss ion thrusters far too readily and without substantiating your arguments. In the first Ars article discussion you say: 'Quick, name a production ion thruster with more than, say, 10 N of thrust. That's what they'd need to place 10 tones in GEO in the "months" they quote. Hint: there isn't one.' You don't support that 10 N number.

But if we stipulate it's correct there are still other problems. The thrust per thruster (1/er?) is mostly irrelevant. The 3 stats that really matter assuming you have a reliable thruster (and we do, look at the DS1 spare thruster test) are specific impulse (Isp), power required and thrust per unit mass. Isp is definitely high, as is power required, but that will clearly come from the solar panels (and put an upper limit on thrust) and thrust per unit mass.

The latter two are the limiting factors on the thrust available to the vehicle. For a fixed specific impulse (which is just exhaust velocity divided by earthside acceleration due to gravity's magnitude), power required should scale linearly with thrust (either by adding more thrusters or by increasing mass throughput of a given thruster). If we look at the HiPeP, assuming an Isp of 9600 seconds, a power required of 39 kW and a thrust of 670 mN, we get 17mN/kW (also 0.058 kW/mN). For 10 N, that means we need 582 kW. PowerSat says they can get 17MW, so power available is not a limiting factor.

That leaves the unit mass of such a thruster. I've had trouble find thrust to mass ratios for ion drives --just the drive units. The best figure I have is from "An Overview of the HiPEP Project" by Elliott, Foster and Patterson, all NASA-Glenn engineers, that sets the thruster mass target at less than 3 kg/kW. I'm not sure what they achieved, but that does push the mass for a 10 N system to 1750 kg. That's quite high, but it's well within the total mass allowance for the PowerSat module. So, it's definitely conceivable that the PowerSat design could have 10 N worth of HiPEP type thrusters.

Fuel will also take up another significant fraction of the mass. Wikipedia, "Delta-V budget", says that the delta V between Equatorial Low Earth Orbit and Geosynchronous orbit is 3.9 km/s. Neglecting gravity losses and applying the rocket equation, we get a propellant mass of 0.45 tons. Turner* says that non impulsive (constantly thrusting) systems suffer gravity losses that reduce the effective specific impulse by a factor as high as 2.3. That gives us a fuel mass of 1.07 tons. Assuming everything is in US tons (907 kg/1 US ton), that's a propellant and engine mass of 2720 kg out of a module mass of 9070 kg. That still fits.

Another problem with your analysis is that you keep using $12000 per pound as a launch cost. (Let's go with $26400/kg to avoid mixing unit systems). Even using the Futron paper you quote "Space Transportation Cost Trends in Price Per Pound 1990-2000," that number only applies to GEO orbits, but you keep using it even when it comes to the PowerSat program, which is supposed to use ion drives to go from LEO to GEO. I guess this is because you'd written off ion drives, but they do seem viable. So, looking at the Futron paper, we see average costs of about $11000/kg for launchers in the 10 ton range already using Western launchers and half that for non Western launchers. Using that data suggests that PowerSat should get a similar or lower price because it plans to build the sats first and then get a launch contract to leverage bulk pricing and because it can launch to the cheapest LEO orbits because it's using ion drives.

3) You've mentioned a couple of collisions in GEO, but haven't substantiated them. I haven't found them, either. The only ones I've found are in LEO.

You've also mentioned the Kessler Syndrome, the increase in space debris in LEO until it becomes unusable. It is a problem, but I consider that an argument for getting Space Solar Power up as soon as possible. Orbitting solar arrays driving lasers and masers can be used to vaporize and/or push space trash out of LEO and out of earth orbit as discussed in the Wikipedia article "Laser broom".

Furthermore, Kessler Syndrome applies to LEO, not GEO. MEO to GEO space is much bigger and much more empty than LEO space. While the PowerSat modules will pass through LEO, they will end up in GEO, so they won't contribute as much to Kessler syndrome and they won't be vulnerable to the current LEO debris environment for very long.

I appreciate you making your posts and stimulating my interests in the discussion. It's been very informative.

--Nathan

*Turner's "Rocket and Spacecraft Propulsion" seems to be a good a reference all around for this sort of thing. A lot of it is available on Google books.

Originally posted by The Real Blastdoor:I live in the Princeton area and I don't see where this "significant room in NJ" is. The land that doesn't have shopping malls or houses on it is generally protected green space...

I haven't been to NJ, but naturally you don't see the undeveloped space. Development tends to happen on the edges of roads, so when you drive around you see lots of buildings. But when you get in the air, or poke around in google maps, you'll probably be surprised at all the green spaces hidden behind buildings.

Anyway you only need 4-10 sq miles-- land that can simultaneously be used for agriculture. Even NJ has that much space free.

Originally posted by The Real Blastdoor:I live in the Princeton area and I don't see where this "significant room in NJ" is. The land that doesn't have shopping malls or houses on it is generally protected green space owned by townships dedicated to not developing the land (good luck navigating the overlapping bureaucracies of local govt in NJ if you want to use that land for anything -- local govt here is insane). The closest area with land that might (maybe) be close to cheap enough is in PA. But even then... I think you'd have to go kind of far into PA to find land that's cheap enough to use for this purpose, and given population growth, I don't know how long it will stay cheap.

The Ars article brings it up, and it's far from groundbreaking (sorry). For decades now concepts keep going around showing crops under the rectenna. Given the current state of agriculture (sorry) some farmers or such might beg for a shot at a lessee. The waste heat, as the article states, may make out-of-season fruit for the Tri-State area more than competitive. Farmers already plow around wind-turbine bases in exchange for a cut.

Don't get me wrong, I'm not seeing this deal take off any time soon. But for accounting reasons, not technical ones.

I just ran the numbers on transfer times using good ol' F=ma. And 10 N of constant thrust should move you from equatorial LEO to GEO (3.9 km/s delta-v) in no more than 40 days, no matter what your specific impulse is. So, Maury, I'd really like to know where you got that 10 N figure from.

For the 8 months PowerSat quoted, it will take no more than 1.7 N. Again, regardless of the specific impulse if you have the fuel to thrust for that long. That reduces the thruster mass of my previous calculation to 298 kg, only 3 percent of vehicle weight. That's starting to sound very reasonable. I think PowerSat may be planning on using technology very much like HiPEP.

As for location, I think the safest place would be offshore. Put it a mile off the coast, so it's still within our waters. We could even put engines on it to make it mobile in the event of a military attack (Power plants are military targets, regardless of whether they're on land or in space).

My question is, how are the microwaves converted into usable electricity?

PowerSat will target markets that have strong renewable power mandates but less favorable options for ground-based solar; the Pacific Northwest

Uh, the PNW already has a pretty reliable source of renewable power in hydroelectricity. I'm not sure if we're reaching the limits of our current system, but considering that it's a lot less expensive and damaging compared to coal plants, and that's what this solar technology is being compared to, I can't even imagine that this technology would be attractive to use up here.

My question is, how are the microwaves converted into usable electricity?

from a book called colonies in space (http://www.nss.org/settlement/ColoniesInSpace/colonies_chap03.html):..."Microwaves are easy to form into a beam and can travel long distances with very little absorption in the atmosphere. They readily penetrate even the thickest clouds and rain to arrive at the receiving antenna, or rectenna. The heart of the rectenna is a system of small dipole antennas, similar to the rabbit ears of a TV set. Each is connected to a device called a Schottky-barrier diode. Microwaves, collected by the dipoles, are converted to direct-current electricity within the Schottky diodes with an efficiency of over 80 percent."